1. Field of the Invention
The present invention relates to a method for bounce suppression of a valve member operated by a piezo actuator during the closing phase in an internal combustion engine and a corresponding device for carrying out the method.
2. Description of Related Art
In internal combustion engines, especially in Otto and Diesel engines, valves control the intake and the discharge of the combustion gases, the valve opening and closing times having a considerable influence on the power output, on the fuel consumption, on low-pollutant combustion and on the running properties of the internal combustion engine at a specified rotational speed. These valves are usually developed as flat-seat valves, in the closed state of the valve, a valve member being accommodated with its valve disk in a valve seat in a precisely fitting and sealing manner. To open the valve, the valve disk is lifted off from the valve seat, and in this context, an annular gap opens, through which the combustion gas is able to flow. The flat-seat valve is driven via the valve spindle, which is a part of the valve member. In modern engines, in order to open and close the valves, piezo actuators are used, which open and close again a valve at high speed. In particular during rapid closing of the flat-seat valve, the valve disk bumps into the valve seat, the sealing surfaces of the two elements striking each other. At higher closing speeds, the impact of the valve disk onto the valve seat leads to an elastic bump, as a result of which the flat-seat valve does not close abruptly, but rather opens slightly and closes again several times after the first closing. This impacting impairs the precision of the closing process, and thereby influences the abovementioned properties of the internal combustion engine in an undesired way. Furthermore, the impacting of the valve disk on the valve seat leads to rapid material wear. In particular, the exhaust valve of an internal combustion engine is especially exposed to corrosive conditions, because the sealing surfaces on the valve disk and the valve seat are exposed to high temperatures and the corrosive effects of the hot and combusted combustion gases.